A process known for the production of semicarbazide uses hydrazine and urea as starting materials. Another known process starts from hydrazine and a cyanate.
Since the raw material hydrazine is expensive, these processes give semicarbazide at high cost, hence are disadvantageous.
Hydrazine is produced by oxidation of ammonia. More specifically, the Raschig, organic, and hydrogen peroxide processes may be mentioned, among others. In any process, however, energy and cost are required for concentration from a dilute solution and for ketazine hydrolysis, for instance, inevitably rendering the product hydrazine expensive.
Hydrazine can also be produced by oxidation of urea. This process is known as the urea process, and the production route to semicarbazide from the thus-obtained hydrazine is as follows: EQU NH.sub.2 CONH.sub.2 +4NaOH+Cl.sub.2 .fwdarw.N.sub.2 H.sub.4.H.sub.2 O+Na.sub.2 CO.sub.3 +2NaCl+H.sub.2 O (1) EQU N.sub.2 H.sub.4.H.sub.2 O+NH.sub.2 CONH.sub.2 .fwdarw.NH.sub.2 CONHNH.sub.2 +NH.sub.3 +H.sub.2 O (2)
The above equations (1) and (2) give the following equation (3): EQU 2NH.sub.2 CONH.sub.2 +4NaOH+Cl.sub.2 .fwdarw.NH.sub.2 CONHNH.sub.2 +Na.sub.2 CO.sub.3 +2NaCl+NH.sub.3 +2H.sub.2 O (3)
The urea process requires sodium hydroxide in large amounts for the production of hydrazine and allows formation of the byproduct sodium carbonate, which requires cost of treatment. Consequently, the hydrazine production cost becomes high.
For producing semicarbazide using the abovementioned urea process, sodium hydroxide and urea are required in large amounts and costs are needed also for the treatment of the byproducts sodium carbonate and ammonia. As a result, the hydrazine production still costs high.